JavaScript Anchoring Utility Libraries

As part of work I've been doing over the last couple months I've created
three JavaScript libraries that implement client-side support for some of
the Web Annotation Data Model selector types on HTML (+ embedded SVG)
documents.

The goals are three-fold:

1) Rewrite Hypothesis anchoring code to be better tested and more clear
2) Expose anchoring utilities to the widest possible audience (no
dependencies on Hypothesis or Annotator code)
3) Experiment with a scripting API for client-side anchoring

These modules expose one class each, all of them implementing an implicit
abstract interface for an anchor that looks like this:

Anchor.fromSelector
Static method to convert from a JavaScript Object to an instance

Anchor.fromRange
Static method to convert from a DOM Range to an instance

Anchor.prototype.toSelector
Method to convert from an instance to a JavaScript Object representation of
a Web Annotation Data Model selector

Anchor.prototype.toRange
Method to onvert from an instance to a DOM Range

Pseudocode for anchoring a selector:

var selector = JSON.parse(data);
// Possibly inspect the type of the selector
var anchor = SomeAnchorType.fromSelector(selector);
var range = anchor.toRange();

Pseudocode for describing a user selection as a selector:

var range = window.getSelection().getRangeAt(0);
var anchor = SomeAnchorType.fromRange(range);
var selector = anchor.toSelector();
var data = JSON.stringify(selector);

These are the libraries:

Fragment Selector: https://github.com/hypothesis/dom-anchor-fragment
Text Position Selector:
https://github.com/hypothesis/dom-anchor-text-position
Text Quote Selector: https://github.com/hypothesis/dom-anchor-text-quote

All of these have been published on npm as alpha versions, which means you
have to specify the version explicitly when installing them for now.

I would appreciate any feedback on these and I hope that they are useful
for implementations or discussion. I will publish 1.0 final versions of
these within the next few days, hopefully after I get positive feedback
from at least a couple readers.

Cheers